Liquid sample loaders are used to load samples into an analytical instrument for measuring various properties of the sample. Examples of analytical instruments are polarimeters for measuring the optical rotation of samples and refractometers for measuring the refractive index of samples.
Often, a laboratory worker loads the analytical instrument manually by injecting the liquid sample into the input port of the instrument with a syringe while watching for excess sample to appear at the output port to verify that the instrument is fully loaded. A tube connected to the output port carries any excess sample to a waste jar.
Once measurements are made by the analytical instrument, the liquid sample is removed. First, the syringe is removed from the input port. Then, one end of a flexible hose with the other end connected to an air pump is attached to the input port. The pump is turned on and the pump's air pressure pushes the sample in the analytical instrument out through the output port and on to the waste jar. To clean the instrument, solvents are injected and removed in a similar manner. Often the final step is to dry any residual solvent by leaving the air hose attached and the pump running for a few minutes.
One disadvantage of the above manual method is the need for a trained operator to load and handle syringes. Also, these syringes are cleaned or treated as a disposable consumable which adds a significant cost to the operation.
At the other end of the spectrum, fully automated liquid sample loaders can be used. In those devices, liquid samples are placed in vials or test tubes in motor driven racks. A robotic needle enters the liquid sample and draws it into the analytical instrument by suction. A light gate/sensor, which is an optical method of detecting the presence of the liquid sample in a transparent tube, is placed near the exit port of the analytical instrument to detect when the loading is complete. Keeping the light gate as close to the exit port as possible minimizes the volume of liquid sample required for each analysis. Cleaning solvents stored in tanks, a system of valves, and an air pump are used to clean and dry the instrument.
While the fully automated loaders offer the convenience of unattended operation, there are many disadvantages such as high cost, high maintenance, and larger size of the equipment, as well as the need to load and clean or dispose of the vials.
In between the above two types of loaders, there are semi-automated loaders for loading samples into the analytical instruments. One such loader is disclosed in U.S. Pat. No. 4,827,746 issued to Kawaguchi, which is incorporated herein by reference and is shown in FIG. 1.
A U-shaped thin oscillating tube 1, which is a part of the analytical instrument is supported by a supporter P. A magnet 2 is attached to tube 1 at the bottom of the U-shape, and oscillates together with the tube. A detection signal, which is an electric signal indicative of the oscillation of magnet 2, is generated by a detection head 3. The density of the liquid which fills tube 1 is calculated on the basis of the detection signal by a detection circuit (not shown). The detection signal is also utilized to drive oscillating tube 1 by driving head 4. One end of tube 1 is open via a sampling tube 5 in a vessel 6 in which the liquid is supplied. The liquid is introduced into tube 1 by a pump 9, which is connected to the other end of tube 1 through a valve 7 and another vessel 8.
In particular, the bottom end of sampling tube 5 draws a liquid sample from vessel 6 by suction from the pump 9. The solenoid valve 7 is closed when the loading is complete to prevent the sample from syphoning back into the vessel 6 during analysis.
While the sample loader of the above type is relatively easy to use and has a moderate cost, there are many disadvantages. First, because the sample is drawn by suction, it may not be able to handle high viscosity samples due to higher forces required or samples with components which may separate and evaporate under suction. While the 746 patent does suggest that the above method could be modified by using pressure, there is no discussion of how this can be achieved. Second, disposal or cleaning of the sampling vessel 6 needs to be done manually by removing the vessel. Third, disposal or cleaning of the outside of the sampling tube 5 needs to be done manually. Fourth, because the solenoid valve 7 is in the sample path, it is exposed to various types of samples or rinse solvents. Valves that are inert to every sample or rinse solvent that might be used can be very expensive. Moreover, valves are subject to damage from particulates and residual material that is allowed to dry within the valve. Fifth, some wasted sample is always left in the bottom of the sampling vessel 5.
Therefore, it would be desirable to provide an improved sample loader and method that overcome the disadvantages discussed above.